Cialis (tadalafil) can be used by patients suffering from erectile dysfunction, i.e. unable to get an erection sufficient for completing sexual intercourse. In case of taking certain alpha-blocker medications, nitrates, nitroprusside, recreational drugs, or being allergic to the active ingredient of Cialis (tadalafil) you must not starting the medicine, as it may cause serious symptoms that could be avoided. Mild side effects are quite common and include dizziness, vision changes, nasal stuffiness, headache, muscle pain, back pain, pain in arms or legs, stomach upset, or flushing. Unless the mild side effects you originally developed go away on their own - report them to your health care provider as soon as possible. Serious side effects can be any of the following: light-headedness, swelling in your hands, ankles, or feet, seizure, vision changes, general ill feeling, fainting, sweating, chest pain, irregular heartbeat, sudden vision loss, sudden hearing loss, shortness of breath, and priapism. Any drugs you are using are supposed to be reported to your doctor before starting the treatment, especially conivaptan, antifungal medications, heart or blood pressure medications, doxazosin, antidepressants, clarithromycin, seizure medications, isoniazid, imatinib, rifampin, erythromycin, HIV/AIDS medicines, diclofenac, and any other ones.